The present disclosure relates generally to welding, particularly to welding high strength steel, and more particularly to welding high strength steel using a motion-controlled electrode to reduce temperatures at the electrode-to-workpiece interface, thereby reducing residual stress and the likelihood of stress cracking in the workpiece.
High strength steels, such as TRIP 800 steel (TRansformation Induced Plasticity steel having a tensile strength of about 800 Mega-Pascals) for example, have utility in the automotive field where the high strength provides benefits, such as fuel efficiency and reduced emission level for example, over lower strength steels since lower gauge materials may be used for the vehicle structure, thereby reducing the vehicle weight while maintaining the structural integrity of the vehicle.
Structures made of high strength steel, however, present a challenge for vehicle assembly, such as the development of stress cracking at the periphery of the weld surfaces in resistance spot welding processes. The non-uniformity of electrical current distribution at the electrode-to-workpiece interface during welding tends to result in localized heat build-up, which causes high residual stresses. The combination of high residual stresses and low ductility may ultimately result in stress cracking in resistance welding of high strength steels.
While existing manufacturing materials and processes may be suitable for their intended purpose, there remains, however, a need in the art for a welding method and apparatus that provides improved control for welding high strength steels, thereby overcoming the aforementioned drawbacks presently associated with welding high strength steels.